There are various ongoing efforts to improve the fuel efficiency of internal combustion engines. One approach involves a start/stop feature, which is implemented in an increasing number of vehicles. In a conventional vehicle, when a vehicle comes to a stop (e.g., at a traffic light or stop sign), the internal combustion engine continues to run at an idle speed, which consumes fuel. In vehicles equipped with a start/stop feature, when the vehicle comes to a stop and other selected conditions are satisfied, the internal combustion engine automatically shuts down to conserve fuel. When the driver releases the brake pedal and/or activates the accelerator pedal, the engine restarts. There may be other selected conditions that can trigger an engine restart.
Some vehicles with a start/stop feature utilize an integrated starter-generator (ISG). The integrated starter-generator combines the functionality of an electric starter motor with that of an electric generator. That is, the integrated starter-generator is capable of subtracting torque from the engine to charge a battery by converting the engine's mechanical energy into electrical energy. The ISG is also capable of converting battery electrical energy into mechanical energy, which can be used to help restart the engine in a start/stop system. An ISG is typically integrated with the crankshaft or mechanically coupled to rotation of the crankshaft via a belt, chain or gear drive system. A belt alternator starter system with an ISG is one example of such a system.